Barcodes are well known and frequently used symbols for identifying products, parts, prices, serial numbers, and many other bits of data. Over the years many different barcodes have been used, including the UPC codes found in grocery stores and the Code 39 barcodes used for many non-grocery items. However, basically the different barcodes are simply alternative ways of encoding information. For example, a narrow bar or space might represent a 0 while a wide bar or space might represent a 1, or a long bar might represent a 0 while a short bar might represent a 1.
Barcodes can differ on how they are sensed. Light, usually in the form of a scanning laser beam, or magnetic energy are commonly used to sense barcodes. A problem with light operated barcodes is that the barcode can become obscured, either with contaminates such as dirt or smudged ink, or by an opaque obstruction, such as a barcode-containing document being inside an envelope or under another document. Magnetic barcodes generally require careful, close placement of a magnetic barcode reader relative to the barcode itself. This can be very difficult to do.
Barcodes sensed by light cannot be placed where they cannot be scanned by a scanning light beam. For example, they cannot be placed on objects within envelopes, and they cannot be embedded beneath the surface of an object such as paper currency. While it might be possible to accomplish this objective with magnetic barcodes, it would be very difficult. The same objective can be accomplished with microwave barcodes using wires of various lengths to encode data, however, this method requires a microwave transmitter and receiver combination that scans multiple frequencies, one resonant frequency for each possible length of barcode wire.
Therefore, a new type of microwave image for data encoding, requiring only a single microwave frequency, would be beneficial. Even more beneficial would be a microwave image that is two dimensional, so that pictorials as well as data can be encoded, and is readable even when placed within opaque materials such as an envelope.
The present invention is directed to a printable microwave image for data encoding comprising a two-dimensional pattern of a plurality of pixels on a surface, wherein each pixel exists in one of two states with respect to radiation in a microwave frequency range. One state would be opaque, preventing transmission of the microwave radiation, and an alternate state would be transparent, permitting transmission of the microwave radiation. The microwave frequency range suitable for use with the present invention ranges from a low frequency of 1 gigahertz to a high frequency of 200 gigahertz. The two-dimensional microwave image is suitable for encoding pictorial images as well as encoding data. An improved detector for reading data encoded microwave images is also provided. The detector comprises two receiving elements connected in series with a diode, such as a Schottky. The total length of the receiving elements equals one half the wavelength of a microwave transmitter used to scan the images. A first quarter wavelength resonator lead has one end connected to one end of the Schottky diode, and the remaining resonator end serves as a first node to which a reader can be attached, wherein the quarter wavelength resonator is one half the length of the total length of the receiving elements. A second quarter wavelength resonator lead is equal in length to the first resonator lead with one end connected to the remaining end of the Schottky diode, and the remaining resonator end serves as a second node to which a reader can be attached.
It is an object of the present invention to provide a printable microwave image system that has the advantage of being insensitive to dirt and ink on the document to which the microwave image has been applied.
It is another object of the present invention to be able to read microwave images that have been placed on documents inside an opaque envelope.
It is still another object of the present invention to provide a microwave image that is two-dimensional and can encode images as well as data.
It is yet another object of the present invention to provide an improved microwave detector for reading microwave images that is smaller, simpler and more efficient than current microwave detectors.
The objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims attached to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects obtained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there is illustrated preferred embodiments of the invention.